The patch titled Subject: selftests/mm: set allocated memory to non-zero content in cow test has been added to the -mm mm-hotfixes-unstable branch. Its filename is selftests-mm-set-allocated-memory-to-non-zero-content-in-cow-test.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Ryan Roberts ryan.roberts@arm.com Subject: selftests/mm: set allocated memory to non-zero content in cow test Date: Tue, 7 Jan 2025 14:25:53 +0000

After commit b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp"), cow test cases involving swapping out THPs via madvise(MADV_PAGEOUT) started to be skipped due to the subsequent check via pagemap determining that the memory was not actually swapped out. Logs similar to this were emitted:

...

# [RUN] Basic COW after fork() ... with swapped-out, PTE-mapped THP (16 kB) ok 2 # SKIP MADV_PAGEOUT did not work, is swap enabled? # [RUN] Basic COW after fork() ... with single PTE of swapped-out THP (16 kB) ok 3 # SKIP MADV_PAGEOUT did not work, is swap enabled? # [RUN] Basic COW after fork() ... with swapped-out, PTE-mapped THP (32 kB) ok 4 # SKIP MADV_PAGEOUT did not work, is swap enabled?

...

The commit in question introduces the behaviour of scanning THPs and if their content is predominantly zero, it splits them and replaces the pages which are wholly zero with the zero page. These cow test cases were getting caught up in this.

So let's avoid that by filling the contents of all allocated memory with a non-zero value. With this in place, the tests are passing again.

Link: https://lkml.kernel.org/r/20250107142555.1870101-1-ryan.roberts@arm.com Fixes: b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp") Signed-off-by: Ryan Roberts ryan.roberts@arm.com Acked-by: David Hildenbrand david@redhat.com Cc: Usama Arif usamaarif642@gmail.com Cc: Yu Zhao yuzhao@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

tools/testing/selftests/mm/cow.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/tools/testing/selftests/mm/cow.c~selftests-mm-set-allocated-memory-to-non-zero-content-in-cow-test +++ a/tools/testing/selftests/mm/cow.c @@ -758,7 +758,7 @@ static void do_run_with_base_page(test_f }

/* Populate a base page. */ - memset(mem, 0, pagesize); + memset(mem, 1, pagesize);

if (swapout) { madvise(mem, pagesize, MADV_PAGEOUT); @@ -824,12 +824,12 @@ static void do_run_with_thp(test_fn fn, * Try to populate a THP. Touch the first sub-page and test if * we get the last sub-page populated automatically. */ - mem[0] = 0; + mem[0] = 1; if (!pagemap_is_populated(pagemap_fd, mem + thpsize - pagesize)) { ksft_test_result_skip("Did not get a THP populated\n"); goto munmap; } - memset(mem, 0, thpsize); + memset(mem, 1, thpsize);

size = thpsize; switch (thp_run) { @@ -1012,7 +1012,7 @@ static void run_with_hugetlb(test_fn fn, }

/* Populate an huge page. */ - memset(mem, 0, hugetlbsize); + memset(mem, 1, hugetlbsize);

/* * We need a total of two hugetlb pages to handle COW/unsharing _

Patches currently in -mm which might be from ryan.roberts@arm.com are

mm-clear-uffd-wp-pte-pmd-state-on-mremap.patch selftests-mm-set-allocated-memory-to-non-zero-content-in-cow-test.patch selftests-mm-add-fork-cow-guard-page-test-fix.patch selftests-mm-introduce-uffd-wp-mremap-regression-test.patch